The present invention relates to a measurement system that measures a physical quantity in a battery pack.
There has been a known battery pack that contains a rechargeable battery and includes a function of calculating a remaining battery capacity of the rechargeable battery. The remaining battery capacity calculated by the battery pack can be used for various purposes; for example, in an electric power tool to which this battery pack is attached and which is operated by electric power from the rechargeable battery, the calculated remaining battery capacity is used to display the remaining battery capacity of the rechargeable battery in a simplified manner.
There have been known various methods of calculating a remaining battery capacity of a rechargeable battery. For example, Unexamined Japanese Patent Application Publication No. 2010-164322 discloses the following technique: a value of a discharge current is detected by an electric current detection unit provided inside assembled cells; the detected value is successively integrated so as to calculate a value of a discharge capacity; the value of the discharge capacity is deducted from a value of a capacity in a fully-charged state, thereby calculating a value of the remaining battery capacity.
Moreover, Japanese Patent No. 3225119 discloses the following technique: in a battery pack, an electric-current detection resistor that detects a value of a charge current and a value of a discharge current from a rechargeable battery is provided; both of a time-integrated value of the detected value of the charge current and a time-integrated value of the detected value of the discharge current are added or deducted, thereby calculating a value of the remaining battery capacity. By taking into account both of the discharge and charge in the above-described manner, the remaining battery capacity can be more accurately calculated.